1. Field of the Invention
The present invention relates to an ITO film having high optical transmittance in a visible light region, ITO powder used in manufacture of the same ITO film, a manufacturing method of the ITO powder, and a manufacturing method of an ITO film. In the present specification, ITO refers to Indium Tin Oxide.
Priority is claimed on Japanese Patent Application No. 2012-132483, filed on Jun. 12, 2012, the content of which is incorporated herein by reference.
2. Description of Related Art
An indium tin oxide film (hereafter referred to as ITO film) used in the conventional art has a band gap of about 3.75 eV and high transparency in the wavelength range of visible light (for example, see Paragraph [0009] of Japanese Unexamined Patent Application, First Publication No. 2009-032699). Therefore, the ITO film has been widely used in a field requiring excellent optical characteristics such as application as a transparent electrode of a liquid crystal display (for example, see Paragraph [0006] of Japanese Unexamined Patent Application, First Publication No. 2005-054273) or a heat shielding material having high heat shielding performance (for example, see Paragraph [0002] of Japanese Unexamined Patent Application, First Publication No. 2011-116623).
Although the conventional ITO film has high transparency in the wavelength range of visible light, absorption edge of the ITO film spread to the visible light region resulting in weak optical absorption near the absorption edge. Due to this phenomenon, the transmittance for the entire wavelength range in the visible light region is decreased, and the ITO film manufactured by a sputtering method tends to show yellowish appearance. The yellowish color is regarded as defective characteristic that deteriorates the appearance of the optical film submitted to visual observation.
On the other hand, the ITO film is also used as a heat cutting film which has recently attracted attention as energy-saving measures in the summer time. In this case, the ITO film is required to shield near infrared rays and have high visible light transmittance.
An object of the present invention is to provide an ITO film having an improved property as an optical film by increasing optical transmittance in the visible light region. Another object of the present invention is to provide ITO powder (indium tin oxide powder) used in manufacturing of the same ITO film. Further, the present invention aims to provide a manufacturing method of such an ITO powder and a manufacturing method of an ITO film.